The present invention relates to an essentially longitudinally oriented magnetic recording medium which has a very small layer thickness and is suitable for high-density recording.
Recently, the recording wavelength has been steadily decreased in order to satisfy the need for increased recording density for magnetic recording media. For example, the recording wavelength for the 8 mm video system is 0.58 .mu.m. This gives rise to the problem of a loss of thickness in signal playback, ie. the playback level does not increase linearly as a function of increasing layer thickness but exhibits a saturation effect. Thus, only a very thin layer is required for short wavelengths.
In order to meet this requirement, magnetic recording media in which a binder-free ferromagnetic metal layer was applied in a very small thickness by means of a vacuum method were developed in the past 10 years. Although these metal evaporated recording media have a small thickness loss and achieve a very high playback level, the mass production of such tapes still gives rise to considerable difficulties in comparison with magnetic recording media in which the magnetic pigments are dispersed in binders. Moreover, these ME tapes change under the influence of atmospheric oxygen.
However, it has recently been possible to meet the requirement for a small layer thickness also by means of a thin magnetic layer in which the finely divided magnetic particles are dispersed in polymeric binder and this layer is cast on a non-magnetic substrate.
Such application methods are described, for example, in U.S. Pat. No. 2,819,186, German Laid-Open Application DE-A 4,302,516, EP 0 520 155, EP 0 566 100 and the German Applications P 44 43 896 and P 195 04 930.
Magnetic recording with high recording density is now predominantly carried out by a digital method. This means that, in contrast to the analog video recording, no sinusoidal signals are recorded and instead the information is recorded on the recording medium by switching over the direction of the current of the recording head. The magnetization pattern produced in such a switching process is referred to as the magnetization transition. However, this transition does not occur abruptly but more or less gradually, for example in the form of a Gauss curve. The playback signal of such a magnetization transition is pulse-like because inductive reading, which is typically used in the video system, is based on differentiation. Since the magnetization transition as described above does not occur abruptly, the read pulses have a certain width, which is usually defined by the PW.sub.50 value. This value indicates the distance on the recording medium between the two points at which the actual signal assumes precisely 50% of the maximum value, as shown in FIG. 1. It is clear that highdensity recording requires very small pulse widths. At the same time, a very large pulse magnitude must be ensured in order to achieve an adequate output level.